Medical humidifier

ABSTRACT

A humidifier for use with a medical respirator having a hot plate type of heating unit entirely separable from a water reservoir which heats the water within the reservoir. The reservoir is provided with an inlet for receiving gas from the respirator and an outlet for delivering heated humidified gas to a patient and a bubble chamber partially submersed in the heated water intermediate the inlet and the outlet and which forms tiny discrete bubbles to be expelled through the water to humidify the gas. A valve means is provided to prevent water in the humidifier from being forced upstream into the respirator yet the valve means introduces relatively minor back resistance to the patient in the event of a cough.

United States Patent 1191 Valenta et a1.

1451 Apr. 23, 1974 MEDICAL HUMIDIFIER [75] Inventors: James D. Valenta,Madison;

Anthony B. Cibul ka, Poynette, both of Wis.; Stephen H. Drabkin,Woodbridge, Conn. [73] Assignee: Airco jlhc, New York, NY.

[22] Filed: June 20, 1972 [21] Appl. No.: 264,694

[52] US. Cl 261/142, 128/193, 261/122 [51] Int. Cl. ..F02m 15/04 [58]Field of Search 261/142, 122, 126, 78 A; 128/186, 188, 194, 198, 192;219/280, 432, 283, 310, 311, 312, 362, 401; 239/338 [56] ReferencesCited UNlTED STATES PATENTS 3,744,771 7/1973 Deaton 261/78 A 3,724,4544/1973 Brown 128/194 3,638,926 2/1972 Melville et al.... 128/192 X3,434,471 31 9 9 Liston 128/192 x 2,709,577 5/1955 Pohndorf et al.239/338 x 2,522,718 9/1950 2,166,574 7/1939 Adolphsen 261/122 X FOREIGNPATENTS-OR APPLICATIONS 1,092,612 11/1960 Germany ..128/194 PrimaryExaminerAndrew R. Juhasz Assistant ExaminerW. R. Briggs Attorney, Agent,or Fir mRoger M. Rathbun; H. Hume Mathews; Edmund W. Bopp [57] ABSTRACTA humidifier for use with a medical respirator having a hot plate typeof heating unit entirely separable from a water reservoir which heatsthe water within the reservoir. The reservoir is provided with an inletfor receiving gas from the respirator and an outlet for deliveringheated humidified gas to a patient and a bubble chamber partiallysubmersed in the heated water intermediate the inlet and the outlet andwhich forms tiny discrete bubbles to be expelled through the water tohumidify the gas. A valve means is provided to prevent water in thehumidifier from being forced upstream into the respirator yet the valvemeans introduces relatively minor back resistance to the patient in theevent of a cough.

17 Claims, Drawing Figures 111' 1 j 76 v l s 9 111 A I 4 54 Q 44 66 a01: 82 l L5 84 60 e S M PATENTEBAPR 23 1574' 3.8061102 SHEET 1 BF 2 FIG.1

PATENTED APR 2 3 I974 SHEET 2 [IF 2 FIG.3.,

FIGA

MEDICAL HUMIDIFIER BACKGROUND OF THE INVENTION This invention relates toa medical respirator apparatus and, more particularly, to a humidifierfor receiving gas from a respirator and heating and humidifyin'g thatgas in order to deliver a warm, saturated gas to the patient.

Humidifying devices are often associated with medical respirators inorder to introduce a predetermined amount of liquid to the gas suppliedto the patient as well as to heat the gas to or near the patients bodytem perature. It is particularly important to heat and humidify the gasto the patient when a tracheotomy tube is employed for any considerableperiod of time. In such case, the gas from the respirator is introduceddirectly into the patients trachea, thereby bypassing the patients nasalpassages which normally both heat and humidify air during inhalation.

Various types of humidifiers have been used in the past and someincluded a hot plate type of heating unit which underlies and providesheat to a water reservoir compartment yet is removable therefrom withoutdraining the water from the reservoir.

In addition, various types of bubble chambers have been used which, ineffect, receive the gas from the respirator and cause it to bubble upthrough heated water to humidify and heat the gas for introduction to apatient.

As a further feature in humidifiers it is advantageous to provide avalve means to prevent water within the humidifier reservoir frominadvertently being forced backward into the respirator itself, where,in such instance a loss of functioning of the respirator could occurtemporarily, or even permanently, cutting off the source of lifesustaining oxygen to the patient. To this end, check valves have beenlocated in the humidifier to prevent the backflow of water, such ascould commonly occur by the patient coughing to force air back into thereservoir. The normal location of such a check valve in prior artdevices has, however, generally cut off all return flow of gas from thepatient so that extreme discomfort would occur to the patient in hiscoughing into a closed system.

The precise location of this check valve is further critical in theevent that the humidifier is inadvertently placed into the respirationsystem in an incorrect manner, that is, the humidifier inlet isconnected to the patient circuit while the humidifier outlet is joinedto the respirator. In this event, the check valve may well prevent anyflow at all through the humidifier, thus the patient, until the error isdiscovered and corrected, may not be receiving any oxygen enriched gasfrom the respirator.

Also, a further desired feature in humidifiers utilized with somerespirators, is a through passage which, in effect, allows some directcommunication between the humidifier inlet and its outlet. The purposeof this passage is to allow a patient triggered respirator upstream ofthe humidifier to instantaneously and positively sense any attempt bythe patient to inhale, whereupon the respirator can be triggered toswitch into its inhala tion phase.

SUMMARY OF THE INVENTION The present invention provides a combination ofdesirable features, including economical construction and convenientassembly and disassembly. The humidifier is quickly and easilydisassembled for cleaning, yet is efficient in use and adequatelyhumidifies and heats the gas from a respirator to be introduced to thepatient. A separable hot plate type of heater is used to underlie andsupport a water reservoir in good heat transfer relationship therewith.The heater is adjustable to maintain the water at a desired elevatedtemperature to control the amount of heat and humidification. Further,inasmuch as the heater is completely isolated from the patient circuit,it does not require special cleansing or sterilization after use witheach patient. In addition, because the heater completely underlies thewater reservoir, a relatively large surface area heater us utilized andoverall heater temperatures may be maintained at relatively low valuesand still adequately humidify and heat the gas to body temperature.

A bubble chamber lies partially submerged within the level of waternormally occupying the water reservoir. The bubble chamber receives thegas from the respirator and channels the gas through a plurality ofsmall apertures to form finely dispersed bubbles, which rise through theheated water to the surface. The gas, thus heated and humidified leavesthe humidifier through an outlet in the water reservoir to the patient.A valve means is located within the gas 'flow passages of the humidifiersuch that water within the humidifier reservoir cannot be forced backinto the respirator. At the same time, the valve means does not preventthe reverse flow of gas from the patient, that is, if the patientcoughs, the return flow of gas does not meet a blocked passage in thehumidifier to cause discomfort in the patient. Instead, the valve meansallows this gas from the patient to continue through the humidifier tobe eventually dissipated in the upstream passages.

As a safety feature, the valve means allows gas to pass through thehumidifier in the event the humidifier is inadvertently connected intothe respirator circuit in reverse position, i.e., the humidifier inletin connected to the patient circuit and, correspondingly, the humidifieroutlet is connected to the respirator. In this incorrect circuitconnection, the present humidifier does not block flow to the patientwhich could result in immediate harm, but allows the free flow of gasfrom the respirator to the patient, however, the gas will not be heatedor humidified. The connection error can safely be recognized byobserving the temperature of gas entering the patient and necessarysteps to alleviate the situation taken without great harm to thepatient.

The present humidifier also includes a bleed passageway which allowsdirect communication between the humidifier inlet and its outlet. Thispassageway allows a patient triggered respirator to be utilized whereinthe patient inhalation sensing device may be upstream of the humidifier.As the patient attempts to inhale, the slight vacuum which is drawn isimmediately communicated through the humidifier to the respiratorsensing means whereby the respirator can react by switching to itsinhalation phase.

The assembly and disassembly of the humidifier is accomplished withrelative ease. The water reservoir and hot plate heater are separableand are held in good heat conductivity by a single securing means whichis easily removable to separate the units. The bubble chamber is securedin place by fairly simple means and its complete disassembly forservicing or cleaning can be accomplished with ease.

BRIEF DESCRIPTION OF THE DRAWINGS.

FIG. 1 is a side elevational view of-the humidifier constructed inaccordance with the present invention.

FIG. 2 is a plan view from above FIG. 1. FIG. 3 is a verticalcross-sectional view of the water reservoir removed from the completedassembly 'of FIG. 1.

FIG. 4 is a vertical cross-sectional view of the plate heater utilizedwith the present invention.

SPECIFICATION Referring to FIGS. 1 and 2, there is shown a humidifierhaving a heater 12 and a reservoir 14. As shown, the heater 12 is of theelectrical hot plate type which is adapted to underlie and support thereservoir 14 when the humidifier 10 is assembled. The heater 12 isadapted to be connected to a conventional electrical source, not shown,such as 110 volt AC potential through the power cord 16. A control meansmay be conveniently located in the base of the heater 12 to vary thetemperature of the heater l2 and preferably includes a projecting knob18 having printed indicia thereupon to indicate the precise location ofthe control and direction of rotation to increase or decrease the heatoutput of the heater 12.

An inlet 20 introduces gas from the respirator to the reservoir 14 andis shaped in a circular upstanding projection to be connected toconventional tubing, not shown, conveying the gas from the respirator.An outlet 22 is provided, similarly shaped as inlet 20, and serves to beeasily connectible to conventional tubing for conveying the heatedhumidified gas from the humidifier 10 to the patient circuit.

The reservoir 14 is firmly attached to the heater 12 by a tie bolt 24which extends through the interior of reservoir 14 and is screwed to theheater 12 such that the reservoir 14 may be easily and convenientlyremoved for cleaning and the like. When the humidifier 10 is assembled,the tie bolt 24 assures that some force holds the reservoir 14 firmlyagainst the heater 12 to insure that good thermal conductivity exists,as will be later explained. I

Turning now to FIG. 4, there is shown, in crosssection, the heater 12utilized with the present invention. Basically the heater 12 is ofconventional design comprising a hot plate 26 in which there is embeddeda resistance heating element 28 providing an overall generally constanttemperature of the heating surface 30. A bottom cover plate 32 isaffixed to the hot plate 26 by means such as a screw 34 and covers theinternal wiring, not shown. A high temperature cut-out 36 abuts theundersurface of the hot plate 26 and serves as a safety device toterminate electrical power to the resistance element 28 in the event itstemperature exceeds a predetermined maximum value. An adjustablethermostat 38 also abuts the undersurface of the hot plate 26 andcontrols the temperature of the hot plate 26 within a predeterminedrange. External control of the thermostat 38 is afforded by means ofshaft 40 which extends through the bottom cover plate 32 to becontrolled by the projecting knob 18. A threaded hole 42 is provided inthe heating surface and is generally located at or near the center ofthe surface 30, the purpose of which will be later explained.

With reference to FIG. 3, the reservoir 14 utilized with this inventioncomprises a housing 44 preferably of a molded transparent plastic suchas polypropylene. The inlet 20 and outlet 22 may be formed into housing44, each of which communicate with the interior thereof. A water chamber46 is formed within housing 44 when the bottom plate 48 is operativelypositioned as shown. The bottom plate 48 is formed of a good heatconducting material such as brass and has joined thereto an upwardlyextending hollow tubing 50 which extends through the top of the housing44 through a hole 52 formed therein. The tubing 50 is firmy affixed tobottom plate 48 such as by a threaded connection which is furthersoldered to insure a watertight joint around the external circumferenceof the tubing 50. An O-ring 54 seals the tubing 50 within hole 52. Theupper end of tubing 50 is provided with screw threads which are adaptedto receive a nut 56 which, when tightened onto the tubing 50, securesthe bottom plate 48 firmly to the housing 44 containing therein thewater chamber 46. A sealing gasket 56 surrounds the outer periphery ofthe bottom plate 48 to seal against a downwardly directed circularprojection 58 of the housing 44.

Within the water reservoir 14 there is positioned a bubble chamberassembly 60. The bubble chamber assembly 60 includes a bubble chamberhousing 62 having external threads 64 which are adapted to bescrewedinto'internal threads 66 formed in the housing 44. By this meansthe bubble chamber housing 62 is suspended firmly from housing 44 withinthe overall reservoir 14. A bottom cover 67 is affixed to the bubblechamber housing 62, preferably by being screwed into the bubble chamberhousing 62 by mating threads at 68.

-Within the bubble chamber housing 62 there is formed a diffuser inletpassage 69 which receives gas from the inlet 20. The diffuser inletpassage 69 extends downwardly and terminates at a distance above thebottom cover 67. A diffuser 70 extends from the periphery of thediffuser inlet passage69 at the bottom end thereof to the lateral innerperipheral surface of the bubble chamber housing 62, forming a lowerchamber 72 within the bubble chamber housing 62. The diffuser may be ofplastic construction having a large plurality of small closely-spacedholes therein. A plurality of apertures 74 are formed in the bubblechamber housing 62 generally toward the upper portion thereof.

A valve means is provided in the bubble chamber housing 62 and, asshown, comprises a plurality of valve apertures 76 radially orientedabout the top of the housing 62. A resilient disc 78 covers each of thevalve apertures 76 and is affixed to housing 62 at its internalcircumference. In practice the disc 78 may be easily assembled by beingsnapped into a circular recess 80 in the bubble chamber housing 62. Ableed orifice 82 extends from inlet passage 69 to allow directcommunication between the inlet passage 69 to the outlet 22 throughapertures 74.

In the operation of the humidifier, the reservoir 14 is filled to withina predetermined level range with water, generally to a level asindicated by the dashed line 84. The heater 12 is turned on and itstemperature adjusted by knob 18 to a predetermined value in order tobring the temperature of the water up to its desired temperature. Afterattaining this temperature, the heater thermostat 38 maintains thattemperature relatively constant or stable. Gas, such as oxygen or oxygenenriched air, is caused to enter the inlet 20 at a positive pressurefrom a respirator. The gas continues downwardly through the diffuserinlet passage 69 and is forced through the water into the lower chamber72 and bubbles upwardly through the diffuser 70 which causes a pluralityof minute bubbles to be formed which bubble up through the warm water,causing the bubbles of gas to be warmed as well as humidified. The gasis thus heated and humidified as it reaches the surface of the waterwithin the bubble chamber housing 62 where it is caused to pass throughthe apertures 74 into the upper interior of the reservoir 14 and leavesthe humidifier through outlet 22 to the patient circuit. Thus, the gasfrom the respirator is both heated and humidified as it passes throughthe humidifier to the patient.

In the event the humidifier is inadvertently connected within thecircuit in a manner opposite of that intended, that is, humidifieroutlet 22 is connected to the respirator and the inlet is connected tothe patient circuit, the humidifier valve means provides a safetyfeature by allowing the free flow of gas from outlet 22 throughapertures 74 and out through the inlet 20 via the valve apertures 76.The resilient disc 78 acts as a check valve which freely allows the flowof gas in the direction from outlet 22 to inlet 20. This is not only asafety feature to allow reverse flow if the humidifier is incorrectlyinstalled, but the resilient disc 78 also allows a reverse flow of gasduring normal operation which may occur by the patient coughing. Theresilient disc 78 freely allows backflow of gas through the valveapertures 76 so that the patient does not feel discomfort by coughinginto a dead ended space.

Since the reservoir 10 may be used with a respirator having a patienttriggering control, an open passageway is provided between the outlet 22and the inlet 20 by a small bleed orifice 82. An attempt by the patientto inhale is thereby signaled directly through the reservoir 10 throughthe outlet 22, apertures 74 and then to the inlet through orifice 82 toa sensing means upstream of the reservoir 10. Thus, a patient triggeringmeans, responsive to a minute vacuum drawn as the patient com mencesinhalation, can be located at the respirator and yet the patient vacuumdrawn is rapidly transmitted directly through the reservoir.

Thus, there is provided a unique, easily disassembled reservoir having areservoir which is separable from the heating unit for ease of cleaning.The reservoir protects the reverse flow of water upstream into therespirator or other apparatus, yet allows a backflow of gas from thepatient for comfort in the event of coughing. As a safety feature, thereservoir may be incorporated into the respirator patient circuit in thereverse of its intended flow position, yet the flow of gas to thepatient is not interrupted so that the patient still receiveslifesustaining oxygen.

Further, the reservoir, when in operation, allows free use of patienttriggering devices to control the respirator.

We claim:

1. A humidifier for heating and humidifying gas received from a medicalrespirator and delivering the gas to a patient circuit, comprising incombination:

a reservoir adapted to contain a quantity of water; heating meansunderlying and supporting said reservoir, said means being adapted tomaintain the water in said reservoir at a predetermined elevatedtemperature;

an inlet in said reservoir for normally receiving gas from saidrespirator and an outlet in said reservoir for normally delivering gasto said patient circuit;

bubble chamber means within said reservoir connected to said inlet anddefining a normal first gas flow path between said inlet and outletwhich at least partially passes through the water in said reservoir,whereby to heat and humidify said gas;

said bubble chamber means including normally closed check valve meanspositioned in said chamber means to define a second gas flow path in thedirection between said outlet and inlet, said second flow path bypassingsaid water, and said check valve being opened to establish said secondflow path by gas pressure at said outlet exceeding the gas pressure atsaid inlet.

2. Apparatus in accordance with claim 1 further including bleed orificemeans providing direct communication between said reservoir inlet andoutlet, whereby patient triggering of devices at said respirator isenabled.

3. Apparatus in accordance with claim 1 wherein said bubble chambermeans includes a diffuser inlet passage connected to said reservoirinlet and passing downwardly to a point beneath the water level of saidreservoir, a lower chamber for receiving the gas flow from said passageand a chamber housing concentric with said passage and connected theretothrough a diffuser plate, said housing being provided with a pluralityof first openings permitting gas flow toward said reservoir outlet.

4. Apparatus in accordance with claim 3 further including a bleedorifice in the wall defining said diffuser inlet passage at a pointabove the water level of said reservoir, said orifice connecting intothe space between said passage and concentric housing thereby providinga direct flow path between said reservoir inlet and said plural openingsof said bubble chamber housing, whereby pressure changes at said patientcircuit may be directly communicated to said reservoir inlet to providetriggering of devices thereat.

5. Apparatus in accordance with claim 3 wherein said check valve meanscomprises a plurality of second openings at the upper portion of saidbubble chamber means, said openings communicating with said reservoirinlet; and flexible flapper valve means biased against said openingsfrom the sides adjacent said reservoir inlet, normally maintaining saidopenings in their closed condition; said second openings communicatingdirectly with said first openings to enable a backflow path between saidreservoir outlet and inlet.

6. Apparatus in accordance with claim 5 wherein said biasing force issufficiently small as to enable said backflow path upon coughing orsimilar disturbance at said patient circuit.

7. A humidifier for use with a heating plate in the heating andhumidifying of gas received from a medical respirator, for delivery ofsaid gas to a patient circuit, comprising in combination:

a reservoir adapted to contain a quantity of water,

and including a liquid-tight chamber and a bottom plate adapted forthermal engagement with said heating plate;

an inlet in said reservoir for normally receiving gas from saidrespirator and an outlet in said reservoir for normally delivering gasto said patient circuit;

bubble chamber means within said reservoir connected to said inlet anddefining a normal first gas flow path between said inlet and outletwhich at least partially passes through the water in said reservoir,whereby to heat and humidify said gas;

said bubble chamber means including normally closed check valve meanspositioned in said chamber means to define a second gas flow path in thedirection between said outlet and inlet, said second flow path bypassingsaid water, and said check valve being opened to establish said secondflow path by gas pressure at said outlet exceeding the gas pressure atsaid inlet.

8. Apparatus in accordance with claim 7 further including bleed orificemeans providing direct communication between said reservoir inlet andoutlet, whereby patient triggering of devices at said respirator isenabled.

9. Apparatus in accordance with claim 7 wherein said bubble chambermeans includes a diffuser inlet passage connected to said reservoirinlet and passing downwardly to a point beneath the water level of saidreservoir, a lower chamber for receiving the gas flow from said passageand a chamber housing concentric with said passage and connected theretothrough a diffuser plate, said housing being provided with a pluralityof first openings permitting gas flow toward said reservoir outlet.

10. Apparatus in accordance with claim 9 further including a bleedorifice in the wall defining said diffuser inlet passage at a pointabove the water level of said reservoir, said orifice connecting intothe space between said passage and concentric housing thereby providinga direct flow path between said reservoir inlet and said plural openingsof said bubble chamber housing, whereby pressure changes at said patientcircuit may be directly communicated to said reservoir inlet to providetriggering of devices thereat.

11. Apparatus in accordance with claim 9 wherein said check valve meanscomprises a plurality of second openings at the upper portion of saidbubble chamber means, said openings communicating with said reservoirinlet; and flexible flapper valve means biased against said openingsfrom the sides adjacent said reservoir inlet, normally maintaining saidopenings in their closed condition; said second openings communicatingdirectly with said first openings to enable a backflow path between saidreservoir outlet and inlet. I

12. Apparatus in accordance with claim 11 wherein said biasing force issufficiently small as to enable said backflow path upon coughing orsimilar disturbance at said patient circuit.

13. A humidifier for heating and humidifying fluid received from amedical respirator and delivering the fluid to a patient circuit, saidhumidifier comprisinga reservoir adapted to contain a quantity of water,heating means underlying and supporting said reservoir,

said heating mean adapted to maintain the water in said reservoir at apredetermined elevated temperature, an inlet in said reservoir forreceiving fluid from the respirator and an outlet in said reservoir fordelivering-fluid to the patient circuit, a bubble chamber within saidreservoir intermediate said inlet and said outlet adapted to heat andhumidify fluid flowing between said inlet and siad outlet, said bubblechamber including normally closed check valve means positioned in saidchamber to define a second gas flow path in the direction between saidoutlet and inlet, said second flow path bypassing said water, and saidcheck valve being opened to establish said second flow path by gaspressure at said outlet exceeding the gas pressure at said inlet, andsecuring means passing vertically centrally through said reservoir andsecured to said heating means whereby said reservoir is securely affixedto said heating means.

14. A humidifier as defined in claim 13 werein said securing meanscomprises a tie bolt extending through the interior of said reservoir,said tie bolt being threadedly engaged to said heating means wherebysaid reservoir is easily completely disconnectable from said heatermeans.

15. A reservoir comprising a housing bottom plate, secured to housingcontaining therein a liquid-tight chamber, a tubing means upwardlyextending through said housing affixed to said bottom plate, a bubblechamber suspended from cover plate within reservoir,

inlet means for introducing fluid to bubble chamber, outlet means incover plate for receiving fluid within reservoir, check valve meansadjacent the inlet located in parallel with the flow of fluid throughsaid bubble chamber and adapted to pass fluid uni-directionally fromsaid outlet to said inlet, bypassing said bubble chamber, bleed orificeproviding direct communicatio between said inlet and said outlet.

16. A humidifier for heating and humidifying fluid received from amedical respirator, said humidifier comprising a reservoir adapted tocontain a quantity of water, heating means associated with saidreservoir adapted to maintain the water at a predetermined temperature,inlet means in said reservoir for receiving fluid from the respirator, abubble chamber in said reservoir adapted to receive fluid from saidinlet and cause the fluid to bubble through the water thereby heatingand humidifying the fluid, outlet means in said reservoir for receivingthe heated and humidified fluid for delivery to a patient circuit, checkvalve means located in parallel with the flow of fluid through saidbubble chamber and adapted to pass fluid uni-directionally from saidoutlet to said inlet when the pressure in said outlet is greater thanthe pressure in said inlet whereby fluid may freely flow from saidoutlet to said inlet, bypassing said bubble chamber.

17. A humidifier as described in claim 16 wherein said check valvecomprises a resilient ring normally covering a plurality of radiallyoriented apertures, said ring adapted to be displaced by a positive flowof fluid from said outlet, whereby the flow of fluid passes through saidapertures.

1. A humidifier for heating and humidifying gas received from a medicalrespirator and delivering the gas to a patient circuit, comprising incombination: a reservoir adapted to contain a quantity of water; heatingmeans underlying and supporting said reservoir, said means being adaptedto maintain the water in said reservoir at a predetermined elevatedtemperature; an inlet in said reservoir for normally receiving gas fromsaid respirator and an outlet in said reservoir for normally deliveringgas to said patient circuit; bubble chamber means within said reservoirconnected to said inlet and defining a normal first gas flow pathbetween said inlet and outlet which at least partially passes throughthe water in said reservoir, whereby to heat and humidify said gas; saidbubble chamber means including normally closed check valve meanspositioned in said chamber means to define a second gas flow path in thedirection between said outlet and inlet, said second flow path bypassingsaid water, and said check valve being opened to establish said secondflow path by gas pressure at said outlet exceeding the gas pressure atsaid inlet.
 2. Apparatus in accordance with claim 1 further includingbleed orifice means providing direct communication between saidreservoir inlet and outlet, whereby patient triggering of devices atsaid respirator is enabled.
 3. Apparatus in accordance with claim 1wherein said bubble chamber means includes a diffuser inlet passageconnected to said reservoir inlet and passing downwardly to a pointbeneath the water level of said reservoir, a lower chamber for receivingthe gas flow from said passage and a chamber housing concentric withsaid passage and connected thereto through a diffuser plate, saidhousing being provided with a plurality of first openings permitting gasflow toward said reservoir outlet.
 4. Apparatus in accordance with claim3 further including a bleed orifice in the wall defining said diffuserinlet passage at a point above the water level of said reservoir, saidorifice connecting into the space between said passage and concentrichousing thereby providing a direct flow path between said reservoirinlet and said plural openings of said bubble chamber housing, wherebypressure changes at said patient circuit may be directly communicated tosaid reservoir inlet to provide triggering of devices thereat. 5.Apparatus in accordance with claim 3 wherein said check valve meanscomprises a plurality of second openings at the upper portion of saidbubble chamber means, said openings communicating with said reservoirinlet; and flexible flapper valve means biased against said openingsfrom the sides adjacent said reservoir inlet, normally maintaining saidopenings in their closed condition; said second openings communicatingdirectly with said first openings to enable a backflow path between saidreservoir outlet and inlet.
 6. Apparatus in accordance with claim 5wherein said biasing force is sufficiently small as to enable saidbackflow path upon coughing or similar disturbance at said patientcircuit.
 7. A humidifier for use with a heating plate in the heating andhumidifying of gas received from a medical respirator, for delivery ofsaid gas to a patient circuit, comprising in combination: a reservoiradapted to contain a quantity of water, and including a liquid-tightchamber and a bottom plate adapted for thermal engagement with saidheating plate; an inlet in said reservoir for normally receiving gasfrom said respirator and an outlet in said reservoir for normallydelivering gas to said patient circuit; bubble chamber means within saidreservoir connected to said inlet and defining a normal first gas flowpath between said inlet and outlet which at least partially passesthrough the water in said reservoir, whereby to heat and humidify saidgas; said bubble chamber means including normally closed check valvemeans positioned in said chamber means to define a second gas flow pathin the direction between said outlet and inlet, said second flow pathbypassing said water, and said check valve being opened to establishsaid second flow path by gas pressure at said outlet exceeding the gaspressure at said inlet.
 8. Apparatus in accordance with claim 7 furtherincluding bleed orifice means providing direct communication betweensaid reservoir inlet and outlet, whereby patient triggering of devicesat said respirator is enabled.
 9. Apparatus in accordance with claim 7wherein said bubble chamber means includes a diffuser inlet passageconnected to said reservoir inlet and passing downwardly to a pointbeneath the water level of said reservoir, a lower chamber for receivingthe gas flow from said passage and a chamber housing concentric withsaid passage and connected thereto through a diffuser plate, saidhousing being provided with a plurality of first openings permitting gasflow toward said reservoir outlet.
 10. Apparatus in accordance withclaim 9 further including a bleed orifice in the wall defining saiddiffuser inlet passage at a point above the water level of saidreservoir, said orifice connecting into the space between said passageand concentric housing thereby providing a direct flow path between saidreservoir inlet and said plural openings of said bubble chamber housing,whereby pressure changes at said patient circuit may be directlycommunicated to said reservoir inlet to provide triggering of devicesthereat.
 11. Apparatus in accordance with claim 9 wherein said checkvalve means comprises a plurality of second openings at the upperportion of said bubble chamber means, said openings communicating withsaid reservoir inlet; and flexible flapper valve means biased againstsaid openings from the sides adjacent said reservoir inlet, normallymaintaining said openings in their closed condition; said secondopenings communicating directly with said first openings to enable abackflow path between said reservoir outlet and inlet.
 12. Apparatus inaccordance with claim 11 wherein said biasing force is sufficientlysmall as to enable said backflow path upon coughing or similardisturbance at said patient circuit.
 13. A humidifier for heating andhumidifying fluid received from a medical respirator and delivering thefluid to a patient circuit, said humidifier comprising a reservoiradapted to contain a quantity of water, heating means underlying andsupporting said reservoir, said heating mean adapted to maintain thewater in said reservoir at a predetermined elevated temperature, aninlet in said reservoir for receiving fluid from the respirator and anoutlet in said reservoir for delivering fluid to the patient circuit, abubble chamber within said reservoir intermediate said inlet and saidoutlet adapted to heat and humidify fluid flowing between said inlet andsiad outlet, said bubble chamber including normally closed check valvemeans positioned in said chamber to define a second gas flow path in thedirection between said outlet and inlet, said second flow path bypassingsaid water, and said check valve being opened to establish said secondflow path by gas pressure at said outlet exceeding the gas pressure atsaid inlet, and securing means passing vertically centrally through saidreservoir and secured to said heating means whereby said reservoir issecurely affixed to said heating means.
 14. A humidifier as defined inclaim 13 werein said securing means comprises a tie bolt extendingthrough the interior of said reservoir, said tie bolt being threadedlyengaged to said heating means whereby said reservoir is easilycompletely disconnectable from said heater means.
 15. A reservoircomprising a housing bottom plate, secured to housing containing thereina liquid-tight chamber, a tubing means upwardly extending through saidhousing affixed to said bottom plate, a bubble chamber suspended fromcover plate within reservoir, inlet means for introducing fluid tobubble chamber, outlet means in cover plate for receiving fluid withinreservoir, check valve means adjacent the inlet located in parallel withthe flow of fluid through said bubble chamber and adapted to pass fluiduni-directionally from said outlet to said inlet, bypassing said bubblechamber, bleed orifice providing direct communication between said inletand said outlet.
 16. A humidifier for heating and humidifying fluidreceived from a medical respirator, said humidifier comprising areservoir adapted to contain a quantity of water, heating meansassociated with said reservoir adapted to maintain the water at apredetermined temperature, inlet means in said reservoir for receivingfluid from the respirator, a bubble chamber in said reservoir adapted toreceive fluid from said inlet and cause the fluid to bubble through thewater thereby heating and humidifying the fluid, outlet means in saidreservoir for receiving the heated and humidified fluid for delivery toa patient circuit, check valve means located in parallel with the flowof fluid through said bubble chamber and adapted to pass fluiduni-directionally from said outlet to said inlet when the pressure insaid outlet is greater than the pressure in said inlet whereby fluid mayfreely flow from said outlet to said inlet, bypassing said bubblechamber.
 17. A humidifier as described in claim 16 wherein said checkvalve comprises a resilient ring normally covering a plurality ofradially oriented apertures, said ring adapted to be displaced by apositive flow of fluid from said outlet, whereby the flow of fluidpasses through said apertures.